Java API

The Java API is an extensive collection of library routines (written in the Java programming language or in native code) that perform basic tasks such as GUI display and manipulation, sorting and countless others.

The libraries make it considerably easier to program in Java than in C++, according to some software development methodologists; however, other experts attribute the difference primarily to the presence of garbage collection because common libraries for other languages often have similar function to the Java API.

Sun holds complete legal control over the APIs that all Java platforms must support. This helps insure high consistency between platforms, at the cost of decreased freedom. As of Java Development Kit v1.3, the various APIs are:

General APIs:

java.io

Routines for normal input and output. This includes streams and filehandling.

java.lang

Catch-all access to the internals of the language, as well as some information on the underlying native system. Classes in java.lang are always available to the programmer, without needing a special import declaration at the beginning of a sourcecode file.

java.lang.ref

Special routines for interacting with the garbage collector. For example, one can create a weak reference, which allows one to refer to an object, without preventing the garbage collector from cleaning it up. This is useful in caches, where if nothing else refers to an object held by the cache, the garbage collector may clean it up at whim.

java.lang.reflection

Routines for using the Reflection API. The main use of Reflection is to call classes and methods just by knowing their names. This supports very dynamic programming, at the cost of not having safe compile-time checks to see if the class actually exists.

java.math

Numerical routines.

java.net

Special IO routines for networks. This includes the ability to easily request HTML pages, as well as other common transactions.

java.text

Parsing routines for strings. Support for different human-readable languages and locale-specific parsing is also included.

java.util

Routines for useful data structures. These data structures aggregate objects, with varying useful properties. Also includes the Collections API, which is a very organized way to handle data structures, influenced heavily by the Design Patterns community.

More specialized APIs are:

java.applet

Routines to create Applets. Applets allow applications to be downloaded over a network and run within a guarded sandbox. Security restrictions may be applied to applets, so they are not allowed to execute potentially hostile code from within the sandbox.

java.beans

Routines to call code dynamically, using the Reflection API.

java.awt

Routines to create basic GUIs. These GUIs use basic windows from the underlying native system.

javax.swing

Swing is a collection of routines that build upon java.awt. It uses 2D drawing routines to exercise greater control over new windows than the underlying native platform normally allows. One cost of this flexibility is that Swing elements may not exist outside of java.awt windows.

Swing is a very rich system in its own right. There is support for "look & feels," so that widgets in the GUI can imitate those from the underlying native system, or a completely fictional one. Also, design patterns permeate the system, especially a modified model-view-controller? pattern, so programming is done cleanly, with good seperation of function from appearance.

However, one inconsistency is that (as of JDK 1.3) fonts are drawn by the underlying native system, and not by Java. This makes it difficult to have utter, complete control of text size, though there are workarounds. In general, layouts should be used, which keep elements within a GUI aesthetically consistent despite minor variations between platforms.